This invention relates to packing elements for use in chemical process equipment. It relates specifically to packing elements of a novel and advantageous design that are particularly useful in separating vapors from entrained liquids while permitting counterflow contact to maximize mass transfer between the vapor and the liquid.
In distillation or fractionation towers in which a liquid and a vapor are contacted in a countercurrent flow to effect mass transfer, the vapor and liquid to some extent travel co-currently as a result of entrainment of the liquid in the vapor. There is a need to separate these components at the end of the passage through the tower to maintain efficient operation. The vapor entrains significant amounts of liquid during its passage, particularly if the vapor moves with a relatively high velocity. Separation of the entrained liquid is very desirable to complete the process and therefore various devices have been designed to accomplish this end.
While effective separation can be achieved by slowing the rate of flow, this is often impractical for reasons of space or efficiency of recycling. It is therefore highly desirable that the separation process be achieved "in-line".
A particularly effective device is described in U.S. Pat. No. 5,683,493 which provides a plurality of packing elements or cells in vertically stacked layers. In each cell an upflowing vapor/liquid mixture enters through slits in the bottom and exits at the top into a cell in the layer above through slits in the bottom of that cell. Thus vapor/liquid mixture enters through slits in the bottom of a first cell and is caused to take on a rotational motion as it rises within the cell. This causes the liquid component to be expelled through slits in the outer wall of the cell into a downcomer connected to second similar cell offset below the first cell in which it meets an upflowing vapor/liquid mixture. Meanwhile the upflowing vapor from the first cell enters through slits in the bottom of a third cell located above the first cell. By having cells in adjacent layers off-set, the flows are caused to mix thus minimizing localized variations. This arrangement however carries with it certain space penalties that are preferably avoided. The present invention provides a packing system with liquid/vapor separation capabilities that comprises a series of identical cells stacked one on top of another which provide a highly compact and yet efficient structure for achieving the separation.